DESCRIPTION: (Investigator's Abstract) Any description of the processes which preserve the color and brightness of objects independently of the illumination must begin with a consideration of light adaptation. The aim of this proposal is to identify these adaptational transformations and show how they affect the brightness and color of lights. The chromatic and brightness induction paradigms will be used to analyze the transition to a steady state of adaptation following a change in background color of intensity. The underlying mechanisms will be classified into either multiplicative or substractive operations. These mechanisms have different effects on color appearance and have been useful in analyzing the processes controlling sensitivity. Both the spatial and temporal properties of these mechanisms will be investigated, in response to both large and small changes such as might occur in normal viewing of complex scenes. The experiments will reveal the properties of the adaptational mechanisms underlying brightness and color constancy, and will show to what extent they involve common mechanisms of adaptation and to what extent separate, parallel mechanisms, with different properties, operate in determining brightness and color.